Postal sorting machines comprise juxtaposed stacking modules adapted in number to the number of sorting destinations with which the machine has to cope.
These modules comprise compactors fed by a conveyor formed by two wheels between which letters are nipped. The conveyor is provided at each compactor with a switch, whose setting allows letters to be diverted towards the associated compactor, as necessary. In the region of each switch and at the bottom thereof there is located a support plate retaining the diverted letters and facilitating their stacking in conjunction with a jogging shoulder, against which the letters abut, thus defining one of the two side edges of the stack. At the front of the building stack, a sliding plate guided by a rod along which it can slide retracts in accordance with the growth of the stack. This sliding plate compresses the stack under the action of a restoring force provided by a spring or counterweight. Inclination of the support plate is necessary in order to obtain a proper stack.
In these sorting machines, the letters stacked on each support plate have to be removed by hand for placing in a corresponding box. This operation is costly because it needs much manual work repeatedly. Moreover it is tricky because the stack is hard to get hold of and can only be moved in sections.
French patent FR 2 552 743 describes a stacking machine whose stacking support bed comprises means cooperating with a matched receptacle in such a manner that, once filled with letters to be dispatched, the complete receptacle can be handled automatically. One embodiment has a sliding bar mechanism. Each of the bars is shaped like a crank and the upper part of the bar mechanism forms the support bed for the stack. By vertical translation and/or rotation, the bar mechanism can be retracted beneath the receptacle, which has suitable apertures. When the maximum size of the stack is detected, the operator holds back the end of the stack corresponding to the last letter stacked and actuates the retracting device for the bar mechanism.
This kind of device requires mechanical and/or electrical retracting members for the support bed, such as an actuator. This mechanism has to be actuated for retracting and accordingly filling of the receptacle and has to be returned to action after positioning an empty receptacle. Moreover it is only when the bar mechanism has been retracted that removal of the full receptacle can be commenced and only when the empty receptacle has been put in position that the bar mechanism can be restored. Besides the installation of a specific mechanism, this device needs a relatively long manipulation time.
Moreover, installing such a device on an existing sorting machine is not easy; the necessary adaptation requires relatively complex changes.
Finally the receptacle needed for this device has a series of longitudinal apertures in its bottom, corresponding to the passage of the bar mechanism over practically the whole length of the box. This receptacle cannot easily be used for another purpose and even in its specific use, letters can fall through the apertures.
The device in accordance with the invention enables these problems to be overcome.